Prosecutors have since uncovered ties between organized crime and the local police and city government of Iguala, a town 125 miles south of the capital, Mexico City. The mayor of the town and its security chief have disappeared, evading warrants for their arrest.

After eight members of the Guerreros Unidos gang were arrested, they tipped off authorities on the location of the mass grave, uncovered Saturday in a poor district on outskirts of Iguala.

"They grabbed 17, took them to the top of a hill in Pueblo Viejo where they have clandestine graves and where they say they killed them," state prosecutor Inaky Blanco said Sunday, according to Agence France-Presse. Blanco cautioned those details haven't been confirmed by investigators. "El Chucky," the gang's feared leader, ordered the hit, but the motive still isn't clear, Blanco added.